1. Field of the Invention
The invention relates to a screw element for the conditioning and processing of plastics or elastomers in a screw-type extrusion machine having screw shafts drivable to rotate in the same direction and at least one pair of meshing screw elements, each screw element having a tear drop shaped cross-section with an outer periphery arcuate ridge that extends longitudinally the entire length of the shaft and at a constant radius from the shaft away from the respective shaft and, in the longitudinal direction, is of linear extension in parallel to the longitudinal axis of the shaft, a radially external screw land section near the housing extending in parallel to the inside wall of the housing with little clearance relative to the latter.
2. Background Art
A device of the generic type known from German published examined patent application 20 52 480 serves as a mixing device to remove volatile components from viscous masses, two mixing rotors being provided which are driven in the same direction and have axially directed, linearly extending paddle-shaped mixing wings, through which good degassing of the mix is to be achieved for the discharge of volatile components. The part of the housing taken by the mixing wings forms the mixing or reaction zone.
German patent 862 668 describes a kneading device having two unidirectionally driven shafts with kneading worms. These kneading worms continuously pass through the housing throughout the entire conveying portion and are single-flighted, i.e. they extend away from the shaft radially asymmetrically in only one direction.
German published patent application 30 11 918 describes a flow mixer having mixing worms and mixing blades following each other and disposed on shafts driven in opposite directions. In this device, uniform mixing is to be achieved and in addition inhomogeneities in polyolefine resin films are to be avoided.
German patent 949 162 relates to a screw-type kneading mechanism with damming elements in the form of screw flights rotating in opposite directions being formed on shafts rotating in opposite directions. European patent 0 160 124 discloses a twin-screw kneader of uniform twist with kneading disks, which has individual kneading zones with actively conveying, offset kneading disks. The individual kneading disks have a comparatively narrow ridge that is to work with as little play as possible relative to the wall of the housing. The kneading elements of this twin-screw kneader are conceived as kneading disks comparatively short in the axial direction, the ridges being of linear extension in the axial direction, i.e. without twist. Only the ridges of subsequent kneading disks can be offset by some angle one referred to the other.